Cards are a common organizing unit for modern user interfaces (UI). At their core, they’re just rectangular containers with borders and padding. However, when utilized properly to group related information, they help users better digest, engage, and navigate through content. This is why most successful dashboard/UI frameworks make cards a core feature of their component library. This article provides an overview of the API that bslib provides to create Bootstrap cards.
Setup code
To demonstrate that bslib cards work outside of Shiny (i.e., in R Markdown, static HTML, etc), we’ll make repeated use of statically rendered htmlwidgets like plotly and leaflet. Here’s some code to create those widgets:
library(bslib)
library(shiny)
library(htmltools)
library(plotly)
library(leaflet)
plotly_widget <- plot_ly(x = diamonds$cut) %>%
config(displayModeBar = FALSE) %>%
layout(margin = list(t = 0, b = 0, l = 0, r = 0))
leaflet_widget <- leafletOptions(attributionControl = FALSE) %>%
leaflet(options = .) %>%
addTiles()Shiny usage
Cards work equally well in Shiny. In the examples below, replace plotly_widget with plotlyOutput() and leaflet_widget with leafletOutput() to adapt them for Shiny server-rendered plots/maps.
Hello card()
A card() is designed to handle any number of “known” card items (e.g., card_header(), card_body(), etc) as unnamed arguments (i.e., children). As we’ll see shortly, card() also has some useful named arguments (e.g., full_screen, height, etc).
At their core, card() and card items are just an HTML div() with a special Bootstrap class, so you can use Bootstrap’s utility classes to customize things like colors, text, borders, etc.
card(
card_header(
class = "bg-dark",
"A header"
),
card_body(
markdown("Some text with a [link](https://github.com)")
)
)Some text with a link
Implicit card_body()
If you find yourself using card_body() without changing any of its defaults, consider dropping it altogether since any direct children of card() that aren’t “known” card() items, are wrapped together into an implicit card_body() call.1 For example, the code to the right generates HTML that is identical to the previous example:
card(
card_header(
class = "bg-dark",
"A header"
),
markdown("Some text with a [link](https://github.com).")
)Some text with a link.
Restricting growth
By default, a card()’s size grows to accommodate the size of it’s contents. Thus, if a card_body() contains a large amount of text, tables, etc., you may want to specify a height or max_height. That said, when laying out multiple cards, it’s likely best not to specify height on the card(), and instead, let the layout determine the height layout_column_wrap().
Although scrolling is convenient for reducing the amount of space required to park lots of content, it can also be a nuisance to the user. To help reduce the need for scrolling, consider pairing scrolling with full_screen = TRUE (which adds an icon to expand the card’s size to the browser window). Notice how, when the card is expanded to full-screen, max_height/height won’t effect the full-screen size of the card.
card(
max_height = 250,
full_screen = TRUE,
card_header(
"A long, scrolling, description"
),
lorem::ipsum(paragraphs = 3, sentences = 5)
)Dolor felis eu facilisis viverra nulla netus magna? Purus primis pellentesque habitant curae aliquet dictumst inceptos tempor lacus dignissim? Molestie sed justo montes nulla natoque vestibulum, accumsan augue sed. Pretium mattis semper aptent massa suscipit eget conubia odio diam. Mus risus dis, curabitur ultricies parturient.
Lorem ac sollicitudin platea, gravida eu quisque. Blandit vulputate turpis suscipit volutpat primis class aptent rhoncus. Nec mi nunc vehicula tempus, facilisis, turpis pellentesque convallis phasellus purus. Eu enim ut mollis pharetra consequat – per turpis felis ligula consequat. Lectus consequat euismod elementum turpis euismod quam vitae, viverra, hac nascetur eu interdum phasellus, rutrum parturient molestie posuere in viverra.
Elit at turpis mi, accumsan varius velit. Proin mi ullamcorper vivamus egestas eros luctus et donec blandit pellentesque elementum habitant. Conubia massa tincidunt orci habitant penatibus dis odio ad magnis! Mollis facilisi lectus laoreet, venenatis lectus magna? Cursus litora tincidunt quisque, laoreet fusce odio auctor habitasse: curae metus: sem integer feugiat integer maecenas vehicula sodales phasellus!
Filling outputs
A card()’s default behavior is optimized for facilitating filling layouts. More specifically, if a fill item (e.g., plotly_widget), appears as a direct child of a card_body(), it resizes to fit the card()s specified height. This means, by specifying height = 250 we’ve effectively shrunk the plot’s height from its default of 400 down to about 200 pixels. And, when expanded to full_screen, the plot grows to match the card()’s new size.
card(
height = 250,
full_screen = TRUE,
card_header("A filling plot"),
card_body(plotly_widget)
)Most htmlwidgets (e.g., plotly, leaflet, etc) and some other Shiny output bindings (e.g, plotOutput(), imageOutput(), etc) are fill items by default, so this behavior “just works” in those scenarios. And, in some of these situations, it’s helpful to remove card_body()’s padding, which can be done via spacing & alignment utility classes.
card(
height = 275,
full_screen = TRUE,
card_header("A filling map"),
card_body(
class = "p-0",
leaflet_widget
),
card_footer(
class = "fs-6",
"Copyright 2023 RStudio, PBC"
)
)Fill item(s) aren’t limited in how much they grow and shrink, which can be problematic when a card becomes very small. To work around this, consider adding a min_height on the card_body() container. For example, try using the handle on the lower-right portion of this card example to make the card taller/smaller.
This interactive example is a bit contrived in that we’re using CSS resize to demonstrate how to make plots that don’t shrink beyond a certain point, but this concept becomes quite useful when implementing page-level filling layouts (i.e., page_fillable()) with multiple cards.
card(
height = 300,
style = "resize:vertical;",
card_header("Plots that grow but don't shrink"),
card_body(
min_height = 250,
plotly_widget,
plotly_widget
)
)Troubleshooting fill
As you’ll learn more about in filling layouts, a fill item loses its ability to fill when wrapped in additional UI element that isn’t a fillable container. To fix the situation, use as_fill_carrier() to allow the additional element to carry the potential to fill from the card_body() down to the fill item.
Multiple card_body()
A card() can have multiple card_body()s, which is especially useful for:
- Combining both resizable and non-resizable contents (i.e., fill items and non-fill).
- Allowing each
card_body()to have their own styling (via inline styles and/or utility classes) and resizing limits (e.g.,min_height).
For example, when pairing filling output with scrolling content, you may want min_height on the filling output since the scrolling content will force it to shrink:
card(
height = 375,
full_screen = TRUE,
card_header(
"Filling plot, scrolling description"
),
card_body(
min_height = 200,
plotly_widget
),
card_body(
class = "lead container",
lorem::ipsum(paragraphs = 10, sentences = 5)
)
)Dolor netus metus quis habitasse aenean faucibus. Aliquet class magnis donec volutpat dui libero. Tristique donec pharetra augue montes torquent conubia pulvinar. Eros congue convallis ac, dictumst praesent magnis, justo tristique, velit senectus neque bibendum natoque. Hac leo tempus pretium tristique facilisis sociis, blandit habitant facilisi, tincidunt taciti!
Dolor aptent porttitor scelerisque in per, hac vulputate? Justo id nulla porta semper, purus semper est per. Risus quam tellus natoque non malesuada tincidunt nullam feugiat sodales interdum vitae vitae! Vel facilisis iaculis neque dictumst quisque posuere lectus et. Parturient aenean erat nisi nostra suspendisse, primis tortor hendrerit vivamus placerat habitant in tincidunt a eros suscipit molestie nisl ac: ultricies lectus quam metus risus ridiculus platea.
Consectetur natoque eleifend phasellus et! Sed nunc habitant porttitor interdum potenti phasellus! Nisl cum hac sapien dui tempus sociis vestibulum arcu vel? Elementum varius gravida lacus primis scelerisque fusce ligula! At suspendisse pretium a sodales donec aenean porta urna, aenean nam enim rutrum, a scelerisque turpis nascetur, parturient sociosqu integer turpis nibh diam aliquam nulla accumsan non facilisis netus torquent.
Sit bibendum ornare bibendum vivamus ullamcorper nisi – malesuada cras at, bibendum erat in. Per pharetra vivamus metus enim hac at dis laoreet mollis. Himenaeos proin dignissim facilisis, ultricies suspendisse placerat sollicitudin commodo aliquet dictum, vehicula molestie. Parturient sociosqu dis nam maecenas netus torquent cubilia, viverra mus orci. Na orci!
Consectetur ultrices placerat ridiculus platea cursus! Nunc eleifend mattis suspendisse: fringilla euismod quam, porta mattis mattis. Velit eu tristique torquent lobortis turpis duis interdum? Natoque sociosqu tempus laoreet pretium ultricies ornare integer semper. Dictum suspendisse pharetra bibendum in cubilia, maecenas platea eu, senectus cum dapibus facilisis conubia.
Dolor cum inceptos bibendum ultrices euismod convallis nam rhoncus. Est placerat justo etiam aenean tristique faucibus, vehicula diam. Accumsan eleifend, mi pharetra vivamus egestas – netus dis sollicitudin mauris lacus viverra habitasse lacus habitant? Porttitor platea auctor sociis vestibulum habitasse vehicula convallis malesuada interdum: lectus tellus neque. Eu etiam accumsan porta, phasellus augue quisque aenean pellentesque.
Ipsum torquent rutrum urna natoque lobortis suspendisse interdum. Rutrum molestie est fusce fermentum tristique taciti, egestas viverra magnis donec, potenti fames. Vivamus netus felis taciti fermentum ligula ultricies euismod: in tristique donec mollis metus. Potenti erat scelerisque hac varius eu leo; est condimentum eget. Montes quam purus sodales mollis torquent nulla iaculis!
Elit nulla facilisi parturient est inceptos: sollicitudin faucibus natoque porttitor nibh. Tempus porttitor tincidunt eget, at accumsan euismod ultricies. Hendrerit malesuada vitae condimentum magnis, ridiculus natoque fusce habitant molestie dictumst commodo odio. Platea per volutpat torquent tempor laoreet proin; inceptos nascetur – class vivamus ridiculus molestie. Velit ut dapibus litora et commodo, egestas vitae.
Consectetur vestibulum, risus duis ad eleifend lacus rutrum suscipit? Potenti ullamcorper ornare pulvinar magnis viverra, velit semper fringilla! Taciti enim proin in risus, lacinia porta magna rutrum. Consequat rhoncus nostra fusce orci imperdiet pharetra sem mus mi imperdiet odio? Volutpat non ullamcorper quisque torquent eget nisi, donec ultricies nunc.
Dolor aliquet eros volutpat porta, curae; vulputate sodales magna habitasse faucibus eu nostra! Mauris volutpat nec nec purus; tincidunt, dapibus eleifend dis dignissim, arcu justo purus? Tristique fames imperdiet sociosqu augue, et elementum hendrerit nascetur elementum! Fermentum urna vulputate vehicula hendrerit potenti etiam: integer fringilla purus. Viverra ultrices erat turpis ante!
Also, when the content has a fixed size, and should not be allowed to scroll, set fill = FALSE:
card(
height = 350,
full_screen = TRUE,
card_header(
"Filling plot, short description"
),
plotly_widget,
card_body(
fill = FALSE,
card_title("A subtitle"),
p(class = "text-muted", "And a caption")
)
)A subtitle
And a caption
Multiple columns
As you’ll learn in column-based layouts, layout_column_wrap() is great for multi-column layouts that are responsive and accommodate for filling output. Here we have an equal-width 2-column layout using width = 1/2, but it’s also possible to have varying column widths.
card(
height = 350,
full_screen = TRUE,
card_header("A multi-column filling layout"),
card_body(
min_height = 200,
layout_column_wrap(
width = 1/2,
plotOutput("p1"),
plotOutput("p2")
)
),
lorem::ipsum(paragraphs = 3, sentences = 5)
)Sit semper tincidunt fringilla curabitur potenti taciti primis lacus sodales nostra in molestie? Aptent curae at luctus congue tristique aptent fringilla eget. Ligula tortor arcu in cubilia, ad dis, vivamus consequat ultrices. Habitasse mattis suscipit erat morbi fermentum suspendisse in? Feugiat feugiat volutpat mauris tellus massa egestas platea eros.
Sit fringilla orci id interdum fusce nisi tincidunt. Leo bibendum erat rutrum pharetra; vivamus mollis cras magna auctor. Scelerisque augue nostra ad porta ultrices sociosqu, ac elementum posuere ac primis justo mollis! Mus per viverra consequat aliquet arcu natoque accumsan bibendum himenaeos nisl ac nulla est? A lacus.
Lorem curae rhoncus platea fermentum conubia fusce quisque penatibus ornare tempus. Fusce non nulla, dictumst faucibus congue habitant tristique odio suscipit morbi. Ultrices a fringilla ultrices erat, massa mollis eu ad himenaeos sem donec! Eu inceptos potenti blandit suspendisse mollis egestas tortor vel vitae vitae. Na vitae!
Multiple cards
layout_column_wrap() is especially nice for laying out multiple cards since each card in a particular row will have the same height (by default). Learn more in column-based layouts.
layout_column_wrap(
width = 1/2,
height = 300,
card(full_screen = TRUE, card_header("A filling plot"), plotly_widget),
card(full_screen = TRUE, card_header("A filling map"), card_body(class = "p-0", leaflet_widget))
)Multiple tabs
navs_tab_card() and navs_pill_card() make it possible to create cards with multiple tabs or pills. These functions have the same full_screen capabilities as normal card()s as well some other options like title (since there is no natural place for a card_header() to be used). Note that, each nav() object is similar to a card(). That is, if the direct children aren’t already card items (e.g., card_title()), they get implicitly wrapped in a card_body().
library(leaflet)
navs_tab_card(
height = 450,
full_screen = TRUE,
title = "HTML Widgets",
nav(
"Plotly",
card_title("A plotly plot"),
plotly_widget
),
nav(
"Leaflet",
card_title("A leaflet plot"),
leaflet_widget
),
nav(
shiny::icon("circle-info"),
markdown("Learn more about [htmlwidgets](http://www.htmlwidgets.org/)")
)
)Sidebars
As you’ll learn more about in sidebar layouts, layout_sidebar() just works when placed inside in a card(). In this case, if you want fill items (e.g., plotly_widget) to still fill the card like we’ve seen before, you’ll need to set fillable = TRUE in layout_sidebar().
card(
height = 300,
full_screen = TRUE,
card_header("A sidebar layout inside a card"),
layout_sidebar(
fillable = TRUE,
sidebar(
actionButton("btn", "A button")
),
plotly_widget
)
)Static images
card_image() makes it easy to embed static (i.e., pre-generated) images into a card. Provide a URL to href to make it clickable. In the case of multiple card_image()s, consider laying them out in multiple cards with layout_column_wrap() to produce a grid of clickable thumbnails.
card(
height = 300,
full_screen = TRUE,
card_image(
file = "shiny-hex.svg",
href = "https://github.com/rstudio/shiny"
),
card_body(
fill = FALSE,
card_title("Shiny for R"),
p(
class = "fw-light text-muted",
"Brought to you by RStudio."
)
)
)
Shiny for R
Brought to you by RStudio.
Flexbox
Both card() and card_body() default to fillable = TRUE (that is, they are CSS flexbox containers), which works wonders for facilitating filling outputs, but it also leads to surprising behavior with inline tags (e.g., actionButton(), span(), strings, etc). Specifically, each inline tag is placed on a new line, but in a “normal” layout flow (fillable = FALSE), inline tags render inline.
card(
card_body(
fillable = TRUE,
"Here's some", tags$i("inline"), "text",
actionButton("btn1", "A button")
),
card_body(
fillable = FALSE,
"Here's some", tags$i("inline"), "text",
actionButton("btn2", "A button")
)
)That said, sometimes working in a flexbox layout is quite useful, even when working with inline tags. Here we leverage flexbox’s gap property to control the spacing between a plot, a (full-width) button, and paragraph. Note that, by using markdown() for the paragraph, it wraps the results in a <p> tag, which means the contents of the paragraph are not longer subject to flexbox layout. If we wanted, we could do something similar to render the actionButton() inline by wrapping it in a div().
card(
height = 325, full_screen = TRUE,
card_header("A plot with an action links"),
card_body(
class = "gap-2 container",
plotly_widget,
actionButton(
"go_btn", "Action button",
class = "btn-primary rounded-0"
),
markdown("Here's a _simple_ [hyperlink](https://www.google.com/).")
)
)Here's a simple hyperlink.
In addition to gap, flexbox has really nice ways of handling otherwise difficult spacing and alignment issues. And, thanks to Bootstrap’s flex utility classes, we can easily opt-in and customize defaults.
card(
height = 300, full_screen = TRUE,
card_header(
class = "d-flex justify-content-between",
"Centered plot",
checkboxInput("check", " Check me", TRUE)
),
card_body(
class = "align-items-center",
plotOutput("id", width = "75%")
)
)Shiny
Since this article is statically rendered, the examples here use statically rendered content/widgets, but the same card() functionality works for dynamically rendered content via Shiny (e.g., plotOutput(), plotlyOutput(), etc).
An additional benefit that comes with using shiny is the ability to use getCurrentOutputInfo() to render new/different content when the output container becomes large enough, which is particularly useful with card(full_screen = T, ...). For example, you may want additional captions/labels when a plot is large, additional controls on a table, etc (see the value boxes article for a clever use of this).
# UI logic
ui <- page_fluid(
card(
max_height = 200,
full_screen = TRUE,
card_header("A dynamically rendered plot"),
plotOutput("plot_id")
)
)
# Server logic
server <- function(input, output, session) {
output$plot_id <- renderPlot({
info <- getCurrentOutputInfo()
if (info$height() > 600) {
# code for "large" plot
} else {
# code for "small" plot
}
})
}
shinyApp(ui, server)Appendix
The following CSS is used to give plotOutput() a background color; it’s necessary here because this documentation page is not actually hooked up to a Shiny app, so we can’t show a real plot.